The present invention relates to the field of communications in general and more particularly to cable modems and methods for using the same.
With the rise in popularity of the Internet and other bi-directional communication services, new demands have been placed upon the existing communications infrastructure to support the provision of such services. One installed system that is capable of supporting such services, is the cable system sometimes referred to as the Cable Television System (CATV) which is typically a coaxial wired connection from a cable system service provider facility to end users. While the CATV system has primarily been used to deliver downstream communications from the cable system to the end users (such as cable television signals), it has the capability to support upstream communications from end users to the CATV system provider. Given the bandwidth limitations of the Public Switched Telephone Network (PSTN) commonly used for communications such as Internet data communications, there have been efforts to provide Internet service over the CATV system. Cable modems have been proposed to support such bidirectional data communications over the cable system at high baud rates rather than through the telephone system. Accordingly, the user may access the Internet over the cable system using a cable modem to provide data rates of 42 million bits per second or higher, particularly as the CATV system in some regions may use fiber optic cabling providing even higher system capacity.
Unfortunately, the demands placed on the upstream side of the cable system to support services such as the Internet are generally much greater than those typically encountered previously with more limited services, such as requesting delivery of pay-per-view movies. The greater volume of information being transmitted places more demands on the available throughput of the upstream side of the cable network. Furthermore, while the downstream side is typically a one-to-many distribution network, the upstream side is a many-to-one distribution network placing further demands on the upstream side of the cable network. Therefore, the sensitivity of the upstream side of the cable network to noise is increased when utilized to support services such as the Internet. This is particularly problematic as one of the largest sources of noise on the cable network is noise ingress from the end user location (such as a subscriber""s home). Noise may enter at the back of television sets, at unterminated splitter ports within the home and at other poorly configured in-house cables which often may not be within the control of the operator of the cable system.
It is, therefore, an object of the present invention to provide cable modems, systems and methods for identifying noise signal sources which may improve the performance of the upstream side of a cable network.
In order to provide for the foregoing and other objectives, cable modems are provided with the ability to measure a noise signal power level on the upstream side of the cable network. The cable modem may be configured to make the signal power measurements at a variety of frequencies and at a selected bandwidth during a specified test time period responsive to a request received from the cable network. Methods and systems are provided for identifying a noise signal source on a cable network including specifying a time window for measurements, the desired measurements and the cable modems from which measurements are desired when the need to initiate a test to identify a noise source is detected. Tests may be initiated based on noise signal measurements by individual cable modems or by the cable services provider which indicate an unacceptable noise level. In addition, the reliability of the test measurements may be improved by not allowing any transmissions on the upstream side during the concurrent test window while cable modems are making the requested measurements. The measurements may then be used to identify which end user location(s) is the source of the noise signal.
In one embodiment of the present invention, a self-testing cable modem is provided which includes a cable modem and a signal measurement circuit. The signal measurement circuit is responsive to the upstream side of the cable network (i.e. channels communicating information from the cable modem over the cable network). The cable modem may include a media access controller coupled to a cable network which has a downstream side to the cable modem and an upstream side from the cable modem. The cable modem in this embodiment further includes a processor coupled to the media access controller and a host interface coupled to a host system. The signal measurement circuit is preferably a signal power measurement circuit.
In a further embodiment of the present invention, the signal power measurement circuit includes a bandpass filter having a selectable center frequency having an input side coupled to the upstream side of the cable network and a power detector coupled to an output side of the bandpass filter. The power detector may be a power integrator. The bandpass filter may also have a selectable bandwidth. The center frequency and bandwidth may be selectable responsive to the processor.
In another embodiment, the processor is configured to receive commands over the cable network specifying a desired center frequency for signal power measurements and a desired bandwidth. The processor further includes means for determining a level of a noise signal on the upstream side of the cable network based on measurements performed by the signal measurement circuit.
In addition, the processor may include means for determining a frequency of occurrence of the noise signal on the upstream side of the cable network based on measurements performed by the signal measurement circuit.
In a further aspect of the present invention methods are provided for identifying a noise signal source on an upstream side of a cable network including cable modems. A test initiation event is first detected. Cable modems selected from the cable modems on the upstream side of the cable network are then identified to participate in a test. Signal power measurements on the upstream side of the cable network are requested from the identified cable modems. The requested signal power measurements are then received from the identified cable modems and at least one of the identified cable modems is identified as the noise signal source based on the received requested signal power measurements.
The test initiation even may be detected by detecting a noise signal level violating a detection criteria on the upstream side of the cable network during normal operating conditions of the cable system. Alternatively, an indication of a test initiation event may be received from at least one of the cable modems over the upstream side of the cable network. The noise signal source may be identified by identifying at least one of the identified cable modems which provided signal power measurements violating a selection criteria as the noise signal source. Furthermore, after the noise signal source is identified, a corrective action for the identified noise signal source may be initiated.
In one embodiment, after the cable modems are identified for the test, a test time window is determined and the request for signal power measurements specifies the test time window for the requested signal power measurements by all of the identified cable modems. In addition, a plurality of the cable modems on the upstream side of the cable network which are coupled to a branch of the upstream side of the cable network which includes at least one of the identified cable modems may be notified that no transmissions on the upstream side of the cable network should be generated during the test time window. The notified plurality of the cable modems may include the identified cable modems and may further include at least one cable modem which is not one of the identified cable modems.
In a further aspect of the present invention, a method is provided for identifying a noise signal source on a cable network. A request for signal power measurements on an upstream side of the cable network at the cable modem is received by the cable modem over a downstream side of the cable network. A signal power is then measured on the upstream side of the cable network at the cable modem and the measured signal power is provided to a remote location over the cable network. The received request for a power measurement may specify a time period for measurement and at least one frequency for measurement and the signal power may be measured during the specified time period and at the specified at least one frequency to provide the measured signal power. In one embodiment, transmissions on the upstream side of the cable network are suspended during the specified time period.
While the present invention has been described above in part with reference to method aspects, corresponding systems are also provided.